Conventional disk positioning mechanisms are illustrated in FIGS. 5A and 5B and 6. A magnetic disk 1 as illustrated in FIG. 6 is loaded onto a turntable 6 as illustrated in FIGS. 5A and FIG. 5B. The turntable is connected to a spindle 7 (FIGS. 5A, 5B) of a stepping motor (not illustrated in the drawing). The turntable 6 comprises a boss portion 6a and a disk placing portion 6b (FIG. 5B). Upon the disk placing portion 6b, a magnet 10 is provided. The magnet 10 acts to draw the magnetic disk 1 (FIG. 6) onto the turntable.
A driving pin 8 is located eccentrically from the center of spindle 7 and is fixed to a plate spring 9. The plate spring 9 is fixed to the boss 6a (FIGS. 5A, 5B).
The magnetic disk 1 is enclosed in a case 2 as illustrated in FIG. 6. A hub 5 is provided at the center of disk 1, and spindle 7 (FIG. 5B) inserts into a hole 3, located at the center of the hub 5 (FIG. 6). On this hub 5, another hole 4 is provided at a predetermined distance from the center of the hub (FIG. 6). During the disk loading process, the driving pin 8 slips into the hole 4.
In such conventional art, loading the disk into the correct position of the disk drive requires the following steps. Initially, disk 1 is placed on the turntable 6. Disk 1 is drawn by magnet 10 by means of its magnetic attractive force and is pressed onto the turntable 6 by means of a presser lever (not illustrated in the drawings). Spindle 7 (FIG. 5B) inserts into center hole 3 of the disk 1 (FIG. 6).
As seen in FIG. 7, as the spindle 7 (FIGS. 5A, 5B) rotates, the driving pin 8 (FIGS. 5A, 5B) rotates without changing its distance from the center of the spindle and moves to position 8a. At this position 8a, the driving pin 8 slips into rectangular hole 4 of the disk 1 (FIG. 6). Driving pin 8 next moves to the center portion 8b of hole 4 and then reaches the corner 8c of rectangular hole 4. During this movement, the distance between pin 8 and the center of the spindle is shortened and the plate spring 9 (FIGS. 5A, 5B) is deflected. At the standard position 8c, the driving pin 8 is securely positioned by the two sides of the hub defining hole 4 that is, sides 4a and 4b, which are disposed at approximately a right angle with respect to each other.
At this point, the deflection of plate spring 9 establishes a reaction force Fn as denoted by the arrow (FIG. 7). Another reaction force, Ft, caused by the friction between disk 1 and its case 2 (FIG. 6) and between disk 1 and the magnetic head, is also exerted in the direction shown by the arrow and substantially perpendicular to reaction force Fn. A resultant force of forces Fn and Ft therefore pushes the driving pin 8 against both sides 4a and 4b of the hub defining hole 4.
Driving pin 8 is thus positioned properly within the disk's hole 4; and accordingly, disk 1 is placed at the standard position.
By the conventional method, however, the plate spring 9 is sometimes deflected prematurely, and the force Fn then acts before the driving pin 8 reaches the standard position 8c (FIG. 7). The normal component Fl (FIG. 8), causing the friction force uFl between the driving pin 8 and the hub 5 (u) denotes coefficient of friction), and the tangential component force F2, of reaction force Fn, (FIG. 8) therefore prevent the disk from positioning correctly. In short, disk 1 is rotated before driving pin 8 reaches the standard position 8c.
Such mis-positioning results in unsatisfactory recording and replaying.
To solve the problems stemming from the premature application of reaction force Fn, one could, in an attempt to reduce the value of the coefficient of friction u (and thus the value of friction force uFl), provide a small bearing for driving pin 8. Further, a reduction of the magnetic force may be employed to further reduce the friction force between the turntable 6 (FIGS. 5A, 5B) and the disk hub (FIG. 6).
The addition of a small bearing, however, results in higher costs; and reduction of the magnetic force causes the disk's hub 5 to slip. In addition, from a production standpoint, the adjustment of the magnetic force is not practical and results in higher costs.